As a result of the end of the Cold War, the nuclear powers face the problem of disposing of stockpiles of plutonium, particularly weapons grade plutonium (WG-Pu) including that recovered from the dismantling of nuclear weapons, as well as plutonium which is naturally bred as a by-product of fission power-generating reactors. It is now felt important to be able to dispose of such plutonium economically to make use of the nuclear potential of the plutonium isotopes in a manner which positively guards against diversion and which results in the creation of a final product that cannot feasibly be used in a weapons system.
Previous studies have generally assessed actinide burning to be an unattractive alternative; however, because of the difficulties that have continued to be encountered with licensing a suitable burial repository, the burning of actinides has now become more attractive. It has been proposed to transmutate nuclear waste using a subcritical mass configuration with a flux of neutrons supplied through a linear accelerator (see Nuclear Technology, 101, January 1993 "Accelerator-Driven Subcritical Target Concept for Transmutation of Nuclear Wastes", Van Tuyle et al., and LA-UR-91-2601 (1991) "Nuclear Energy Generation and Waste Transmutation Using an Accelerator-Driven Intense Thermal Neutron Source", Bowman et al., the disclosures of which are incorporated herein by reference). The Phoenix concept proposed in the 1993 article focuses on the disposal of wastes that have been generated in thermal power-generating reactors, particularly upon long-lived radioactive actinides obtained from light-water reactors (LWRs); the concept would employ a large linear proton accelerator (Linac) and would operate using a liquid sodium coolant system to generate power through a steam generator. However, this concept involves removal and reprocessing of the "nuclear fuel" at 2-year intervals, as well as removal of plutonium (a potential power source), and thus far, it has remained only in the conceptual stage both because of the expense and the length of time required.
More recently, scientists from the Los Alamos National Laboratory have proposed the use of nonaqueous systems for the accelerator-driven transmutation of waste, as well as for the accelerator-based conversion of fissionable nuclides in spent reactor fuel. The proposed systems are based upon the circulation of fluoride salt systems through a core region where an accelerator-driven neutron flux is created; heat exchange outside the region of the core would generate usable energy in order to produce electrical power to offset the cost of operation. However, the proposed system requires a 10-year cycle to produce 90% burnup of all plutonium isotopes, and because of the need for constant circulation of a flowing stream, the system would have potential for clandestine diversion of the flowable plutonium salts. Moreover, it would also be subject to the considerable safety considerations involved in circulating highly radioactive material including fission products having high levels of radioactivity.
As a result, the search has continued for more feasible and more attractive ways for economically disposing of plutonium in a manner which renders it incapable of thereafter being employed to create a nuclear detonation.